Mugunth Kumar and Rob Napier have delivered an impressive book packed to the top
with all sorts of tips and tricks that you’ll want to know for iOS development.
iOS 5: Pushing The Limits exposes the details of Xcode schemes, KVO in
practice, handling multiple devices and platforms, and error handling better
than other books I’ve read to date.

It’s not a beginner’s book. I’d recommend it for devs who’ve already built apps
but want to better understand Apple’s conventions and the tools at their
disposal.